Accurately calculating an aircraft's weight and center of gravity (CG) before flight is necessary to comply with certification limits established by the aircraft manufacturer for a given aircraft. These limits include both weight and CG limits. By complying with these limits and operating under the procedures established by the aircraft manufacturer, an operator is able to meet the weight and balance requirements specified in the Airplane Flight Manual (AFM). Typically, an operator calculates takeoff weight by adding the operational empty weight (OEW) of the aircraft, the weight of the passengers, cargo payload, and the weight of fuel. When using average weights for passengers and bags, the operator must be vigilant to ensure that the weight and balance control program reflects the reality of aircraft loading.
To comply with FAA regulations, each operator must construct a “loading envelope” applicable to each aircraft being operated. The envelope will include all relevant weight and balance limitations. It will be used to ensure that the aircraft is always operated within appropriate weight and balance limitations, and will include provisions to account for the loading of passengers, fuel, and cargo; the in-flight movement of passengers, aircraft components, and other loaded items; and the usage or transfer of fuel and other consumables. The operator must be able to demonstrate that the aircraft is being operated within its certificated weight and balance limitations.
In long-established prior approaches, an operator curtails the manufacturer's loading limitations to account for loading variations and in-flight movement that are encountered in normal operations. For example, if passengers are expected to move about the cabin in flight, the operator must curtail the manufacturer's CG envelope by an amount necessary to ensure that movement of passengers does not shift the aircraft's CG outside its certified envelope. If the aircraft is loaded within the new, curtailed envelope, it will always be operated within the manufacturer's envelope, even though some of the loading parameters, such as passenger seating location, are not precisely known.
In some cases an aircraft may have more than one loading envelope for preflight planning and loading. Each envelope must have the appropriate curtailments applied for those variables that are expected to be relevant for that envelope. For example, an aircraft might have separate takeoff, in-flight, and landing envelopes. Passengers are expected to remain seated in the cabin during take-off or landing. Therefore, the takeoff and landing envelope does not need to be curtailed for passenger movement.
Upon determination of the curtailed version of each envelope, the most restrictive points (for each condition the operator's program will check) generated by an “overlay” of the envelopes will form the aircraft operational envelopes. By restricting operation to these “operational envelopes,” compliance with the manufacturer's certified envelope will be ensured in all phases of flight, based upon the assumptions within the curtailment process.
Some examples of common loading curtailments to the manufacturer's loading envelope are now provided. Operators using an approved weight and balance control program include curtailments appropriate to the operations being conducted. Each of the items mentioned below is an example of a single curtailment factor. The total curtailment of the manufacturer's envelope is computed by combining the curtailments resulting from each of these factors.
As a first example, the operator accounts for the seating of passengers in the cabin. The loading envelope does not need to be curtailed if the actual seating location of each passenger is known. If assigned seating is used to determine passenger location, the operator must implement procedures to ensure that the assignment of passenger seating is incorporated into the loading procedure.
If the actual seating location of each passenger is not known, the operator may assume that all passengers are seated uniformly throughout the cabin or a specified subsection of the cabin. If this assumption is made, the operator curtails the loading envelope to account for the fact that the passenger loading may not be uniform. The curtailment may make reasonable assumptions about the manner in which people distribute themselves throughout the cabin.
As a second example, the operator's curtailed loading envelope accounts for the effects of fuel. The following are examples of several types of fuel-related curtailments:
(1) Fuel density. A certain fuel density may be assumed and a curtailment included to account for the possibility of different fuel density values. Fuel density curtailments only pertain to differences in fuel moment caused by varying fuel volumes, not to differences in total fuel weight.
(2) Fuel movement. The movement or transfer of fuel in flight.
(3) Fuel usage in flight. The burning of fuel may cause the CG of the fuel load to change. The effect of fuel burning down to the required reserve fuel or to an acceptable fuel amount established by the operator should be accounted for. A curtailment is included to ensure that this change does not cause the CG of the aircraft to move outside of the acceptable envelope.
As another example, the operator's curtailed CG envelope accounts for the effects of galley and lavatory fluids. These factors include such things as use of potable water in flight, and movement of water or lavatory fluids.
The operational envelope also accounts for the in-flight movement of passengers, crew, and equipment. This may be done by including a curtailment equal to the moment change caused by the motion being considered. It may be assumed that all passengers, crew, and equipment are secured when the aircraft is in the takeoff or landing configuration. Standard operational procedures may be taken into account.
Examples of items that can move during flight include the following:
(1) Flight deck crew members moving to the lavatory.
(2) Flight attendants moving throughout the cabin.
(3) Service carts moving throughout the cabin.
(4) Passengers moving throughout the cabin.
(5) Passengers moving to the lavatory.
If the manufacturer has not already done so, the operator also accounts for the movement of landing gear, flaps, wing leading edge devices, or any other moveable components of the aircraft.